1. Field of the Invention
The present invention relates generally to processing signals in circuits and in particular to a method and apparatus for translating a signal from one voltage domain to another voltage domain in circuits.
2. Description of the Related Art
In designing and producing devices, such as processors and for other applications, multiple supply voltages are typically present. Analog circuits typically require higher voltage supplies, AVDD, than logic circuit voltage supplies, VDD. It is desirable to have reduced or low voltages to reduce the amount of power consumed by the logic circuits in a chip. Higher power supply voltages are desirable for analog circuits because many of these types of circuits do not perform well at lower voltages. Additionally, different power supply voltages are present for input/output boundaries because these interfaces often times are designed to be compatible with older products, which may run at higher voltage power supplies. These different power voltage supplies result in devices having mixed voltages.
In using these mixed voltage devices, an interface is designed to send signals from one voltage domain to another voltage domain. Level shifter circuits are currently used for translating signals between power boundaries and mixed-voltage systems. Level shifters are commonly found in mixed signal, analog, and digital circuits, such as phase lock loops and input/output circuits. With respect to signals and their widths as clock frequencies and data rates increase, it becomes progressively more difficult to control a duty cycle since the signal distortion due to process and environment becomes a much more significant component of the bit or cycle time. Furthermore, power supply adjustments, both active and passive, used for power management or speed sorting make circuit optimization of a duty cycle difficult because the design requirement space becomes so broad. Conventional high frequency level shifter designs may use alternating current (AC) coupling techniques or trimming techniques to improve performance over a wide set of application conditions. However, area, cost, and additional test time in manufacturing can make these methods impractical.
Therefore, it would be advantageous to have an improved method and apparatus for translating signals between different components in a mixed voltage system.